Dr Dharmalingam Prabhakaran

Abstract:

Using ultrafast optical-pump terahertz-probe spectroscopy (OPTP) and ultrafast terahertz emission spectroscopy, we showcase the electron and hole dynamics in Cd3As2 nanowires (NWs), a well-known 3D Dirac semimetal a subgroup of the newly discovered . A temperature-dependent photoconductivity measurement was carried out yielding an incredibly high electron mobility ~ 16,000 cm2/Vs at 5K. Strong THz emission due to helicity-dependent surface photocurrents was also observed for both nanowires and single crystal (SC) which is highly desirable for devices such as THz sources.

Abstract:

The isolated susceptibility may be defined as a (nonthermodynamic) average over the canonical ensemble, but while it has often been discussed in the literature, it has not been clearly measured. Here, we demonstrate an unambiguous measurement of at avoided nuclear-electronic level crossings in a dilute spin ice system, containing well-separated holmium ions. We show that quantifies the superposition of quasiclassical spin states at these points and is a direct measure of state concurrence and populations.

Abstract:

Recent theoretical proposals have argued that cobaltates with edge-sharing octahedral coordination can have significant bond-dependent exchange couplings thus offering a platform in 3d ions for such physics beyond the much-explored realizations in 4d and 5d materials. Here we present high-resolution inelastic neutron scattering data within the magnetically ordered phase of the stacked honeycomb magnet CoTiO3 revealing the presence of a finite energy gap and demonstrate that this implies the presence of bond-dependent anisotropic couplings. We also show through an extensive theoretical analysis that the gap further implies the existence of a quantum orderby-disorder mechanism that, in this material, crucially involves virtual crystal field fluctuations. Our data also provide an experimental observation of a universal winding of the scattering intensity in angular scans around linear band-touching points for both magnons and dispersive spin-orbit excitons, which is directly related to the non-trivial topology of the quasiparticle wavefunction in momentum space near nodal points.

Abstract:

Recent theoretical proposals have argued that cobaltates with edge-sharing octahedral coordination can have significant bond-dependent exchange couplings thus offering a platform in 3d ions for such physics beyond the much-explored realisations in 4d and 5d materials. Here we present high-resolution inelastic neutron scattering data within the magnetically ordered phase of the stacked honeycomb magnet CoTiO₃ revealing the presence of a finite energy gap and demonstrate that this implies the presence of bond-dependent anisotropic couplings. We also show through an extensive theoretical analysis that the gap further implies the existence of a quantum order-by-disorder mechanism that, in this material, crucially involves virtual crystal field fluctuations. Our data also provide an experimental observation of a universal winding of the scattering intensity in angular scans around linear band-touching points for both magnons and dispersive spin-orbit excitons, which is directly related to the non-trivial topology of the quasiparticle wavefunction in momentum space near nodal points.

Abstract:

We characterize experimentally and theoretically the high-energy dielectric screening properties of the prototypical correlated metal SrVO3. The dynamical structure factor measured by inelastic x-ray scattering spectroscopy as a function of momentum transfer is in very good agreement with first-principles calculations in the adiabatic local-density approximation to time-dependent density-functional theory. Our results reveal the crucial importance of crystal local fields in the charge response function of correlated materials: They lead to depolarization effects for localized excitations and couple spectra from different Brillouin zones.